Service brake diaphragms are used in brake actuators operated by fluid pressure, such as actuators found in air braking systems of trucks, trailers, trains, and other heavy-duty vehicles. These air brake systems typically are actuated by means of an actuator assembly operated by the selective application of compressed air.
In a typical service brake actuator, the air-operated brake housing is divided into a pressure chamber and a pushrod chamber. The pressure chamber is fluidly connected to a source of pressurized air and the pushrod chamber mounts a piston or pushrod, which is coupled to the brake assembly, whereby the introduction and exhaustion of pressurized air into the pressurized chamber reciprocates the pushrod into and out of the housing to apply and release the operating brakes.
One known problem in association with service brake actuators of this design is that the piston of an actuator is known to slip, and to move. During wet weather, water mixed with road oil and dirt migrates between the piston and the diaphragm, and acts as a lubricant. The piston can slide radially out of center position, which can restrict the actuator stroke and/or reduce the force output of the actuator. This presents a problem as the service brake will not work as efficiently as under normal conditions, which can lead to longer stopping distances, and eventual malfunction of the service brake. Prior art designs have done little to solve this problem except to straighten the wall of the diaphragm and add grooves. This effect changes the force output curve for the actuator. Optimally, the force output curve should be as flat as possible for maximum stroke actuation. However, straightening the wall makes the force output curve sideways S shaped. Prior art designs have considered the removal of debris as only a secondary concern. These designs are limited as they do not efficiently remove excess debris from the interior surface of the diaphragm as well as also correct misalignment of the piston.
Typically, diaphragms for service brake actuators are made from two layers of rubber sandwiching a layer of fabric. Diaphragms in service brake actuators are generally supported at their periphery between the two housings of the actuator. Upon introduction of a fluid pressure on one side of the diaphragm, the diaphragm moves a push plate or piston to actuate a braking mechanism. The diaphragm is returned to its normal position when compressed air is released, a small return spring returning the pushrod and diaphragm into the normal position.
Diaphragms for brake actuators generally are cup shaped with a bottom wall or base merging into a conical sidewall. The conical sidewall terminates at a rim which is clamped between an upper and lower portion of a housing unit. A force is exerted by the diaphragm upon a piston or push plate, and the diaphragm is typically in direct contact with the piston. Problems occur when material ends up between the piston and the diaphragm, limiting the direct touching between the diaphragm and piston, and causing the piston to slide radially out of the center position. This can restrict the actuator stroke and/or reduce the force output of the actuator.
It is thus desirable to develop a diaphragm for a brake actuator that that helps remove waste material from the diaphragm and limits the radial movement of the piston from the center position. It is also desirable to help positively locate the piston in the diaphragm during assembly, as shown by the embodiments of the present invention.